Field of the Invention
The present invention relates to a numerical controller, and more particularly, to a numerical controller capable of automatically stopping an operation in an appropriate block if a spindle is worked beyond the continuous rated output of a spindle motor.
Description of the Related Art
Conventionally, if a spindle is worked beyond the continuous rated output of a spindle motor, the time (machining continuable time) during which machining can be continued in current cutting conditions is estimated based on the temperature, current value, load data, and the like of the spindle motor. The estimated machining continuable time is displayed on a screen, as shown in FIG. 4. If the spindle is worked beyond this machining continuable time, an overheat alarm is generated to stop an operation.
There is a problem, for example, that a machined surface may be damaged if the operation is stopped in the middle of cutting due to the generation of the overheat alarm. When the continuous rated output is exceeded during the machining, therefore, an operator determines whether or not a program can be performed to the last within the machining continuable time. If it is then determined that the program can be performed only halfway, the operation must be stopped in a block that has no influence on the machining. Normally, however, the block up to which the machining can be performed within the machining continuable time cannot be located, so that it is difficult to determine (or identify) a block in which the operation is stopped.